This invention relates to physiological devices such as pacemakers, muscle stimulators and the like and, in particular, implantable devices having means for sensing given natural events in the patient or events produced by the device, and having means for obtaining and delivering histogram data concerning such events.
Pacemaker design has evolved very rapidly over the last several years. There has been a great advance in the area of programmability of pacemakers, to enable them to be programmed to control pacemaker operation, to work with different selectable operation parameters, and to work in different fundamental modes. Likewise, other physiological devices such as muscle stimulators, artificial drug injectors and the like have undergone substantial advances. In the area of programmable pacemakers, microprocessors are now utilized as a central means for providing flexible programming and control of the pacemaker operation. See, for example, European Patent Application 81108940.8, assigned to the same assignee, which is incorporated herein by reference. As disclosed there, the microprocessor can be incorporated into a pacemaker design for carrying out desired control subroutines, interrupts, and receipt and use of program data transmitted from a location external to the implanted pacemaker. Further, the speed and increased flexibility of microprocessor control enables cycle to cycle adjustments, permitting pacer design to optimize one or more selected parameters, such as pacer rate and escape interval, in view of sensed cardiac conditions.
While adaptive pacemaker control has been accomplished to a great degree in the pacemaker field, as disclosed in the above referenced EPO patent specification, relatively little development has taken place in the area of providing diagnostic information to the physician or user of the device, particularly in the case of implanted devices. One reason for this has been the prior limitation on the ability of an implanted device to accumulate and store sufficient quantities of data to provide meaningful information. For example, in the pacemaker area, systems have been developed which are able to transmit to the physician information about the current pacer operation, including such parameters as pacing rate, stimulus pulse level, refractory interval, etc. However, very little has been done in accumulating and making available device-patient data over any extended period of time, which the physician can use for diagnostic purposes. It is evident that if the physician were to have available a more complete history of the device operation and the patient response thereto, more intelligent judgment could be reached concerning the programming of the on-going device operation. Accordingly, there remains a substantial need, which this invention meets, for an implanted physiological device with means for recording events and parameters related thereto, and assembling data representative of such recorded information in such a way that it can be efficiently transmitted for external display and use.